Mechanisms by which abnormal fetal development, or teratogenesis occurs are not understood. We hypothesize that abnormal induction of the low molecular weight stress protein, hsp27 during embryogenesis is a significant cause of teratogenesis. Because birth defects affect significant numbers of infants and result in considerable costs to the individual, the family and society over a long period of time understanding what may be a significant mechanism for teratogenesis would be extremely beneficial. Toxic agents that cause abnormal embryonic development are called teratogens and a number of teratogens specifically induce the synthesis of a low molecular weight heat-shock or stress protein in Drosophila cells. A similar stress protein, hsp27, is expressed in mammalian cells in mammalian cells also hsp27 synthesis is greatly induced by a variety of teratogens including heat oxidants anoxia heavy metals, estrogens, retinoids, ethanol and other teratogens. Hsp27 is believed to function to affect microfilaments. Altering microfilament function during critical stages of development may disrupt development and result in teratogenesis. Thus, altered microfilament function resulting from abnormal induction of hsp27 synthesis as a result of the toxic action of a teratogen may cause teratogenesis. The hypothesis to be tested is that abnormal induction of hsp27 during embryonic development result in abnormal development or teratogenesis. To test this hypothesis, we will develop transgenic mice in which synthesis of hsp27 can be specifically controlled without induciton of other stress proteins and in the absence of possible side effects resulting from treatment of animals with teratogens or toxicants. First, murine embryonic stem (ES) cells will be stably transfected with an inducible hsp27 expression system. ES cell lines will be developed in which the synthesis of sense or antisense hsp27 mRNA can be induced, thus permitting the amount of hsp27 in the cells to be controlled. The ES cells will then be used to produce transgenic mice in which embryogenesis can be studied in vivo and in vitro. Studies of embryonic development will consist of inducing the synthesis of sense or antisense hsp27 mRNA in the transgenic animal embryos (using a non-toxic inducer) at critical times during fetal development and then observing whether development is altered. It os expected that in animals induced to express sense hsp27 mRNA expression of hsp27 protein will increase above normal and lead to abnormal development in animals induced to express antisense hsp27 mRNA hsp27 protein synthesis will be inhibited and to effect on development is expected. Results of these studies are anticipated to show that abnormally increased expression of hsp27 during embryogenesis results in abnormal development. These studies should provide valuable new information concerning the mechanism of teratogenesis and the role of hsp 27 in embryonic development and organogenesis.